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Varga News:
September 2010
As I assume many of you know, several people worked on
the resolution of a vertical stabilizer spar crack issue that resulted in
the latest Service Bulletin and Airworthiness directive.
This episode of the news will discuss the process that got us
from discovery of a serious problem to fixing it but first, we appreciate that
Brian Tetrault would like to acknowledge and thank those responsible for the
effort that it took to get his airplane back into the air again and to get yours
repaired and flying safely again...
Vertical stabilizer spar
reinforcement
As the owner of the Varga with the first vertical stabilizer
spar crack, I wanted the Varga Community to know how much effort and
tireless volunteer work went into finding a fix for our birds. I have asked Max Bishop to publish
this in the next newsletter unedited as I believe he would tend to minimize
his part in achieving the end results.
The driving forces were Lee and Pat Beery and Max
Bishop. It started on July 6th,
2009 and finished up administratively at least on the 23rd of
February, 2010. There were one
hundred and seventy pages of correspondence, twenty eight photographs,
thirty four diagrams, an FAA Airworthiness Concern Sheet, an FAA Service
Bulletin and an FAA Airworthiness Directive. The effective date of the AD is
March 24th, 2010.
Lee and Max drew from their many years of
experience in the industry. They
tackled the problem and were steadfast in pursuit of an equitable solution. Their emails showed up on federal
doorsteps practically each day.
Tom and Tina Wasson of Tom’s Aircraft Enterprises
and Steve Colvertson of Steve’s Aircraft Repair both at Lampson Field in
Lakeport, CA. gave much with their insight and innovative thinking. Loren Perry, the current Type
Certificate Holder, published the service bulletin that Lee and Max wrote.
On the Federal side were Brook Stewart of the
Sacramento FSDO, Hal Horsburgh and Cindy Lorenzen of the Aircraft
Certification Office in
Atlanta
. For the FAA to approve of this
fix, this quickly, all the key players had to keep the lines of
communication open and the exchange of information flowing. We thank them.
For a certain few, this was a labor of love and to
them we owe a great deal.
Brian Tetreault N1901A
In addition to the thanks from Brian, Maintenance Item
#25 has been added in which Lee Beery has written a
short synopsis of the events and his own thank you for help along the way to the
eventual creation of the Airworthiness Directive.
MAINTENANCE
ITEM
#25 MARCH
2010
(by Lee Beery)
This Maintenance Item is to give the VG 21 members some
insight into the new AD 1020-04-14. As
you recall in the last NL, Max reported the problems found on the vertical
stabilizer on several planes. I
will tell you briefly what transpired.
Being a licensed mechanic, I must report
such findings to the FAA, which I did, and they promptly grounded the two
planes [Brian Tetrault and Lee Beery's]
. The FAA Designated Airworthiness
Representative for our area said the repair was beyond his authority and
directed us to the FAA Designated Engineering Representative [DER]. The
DER wanted $1600.00 for the fix on the primary aircraft and then $800 each for
every aircraft that was repaired after that.
This left us with paying a huge price for his service or doing our own
design work and getting FAA approval by using a “one time” field approval,
a form 337. It took four
submissions of a 337 and 60 days. The actual time to disassemble the tail,
fabricate, and install the doubler, reassemble the tail and check everything
out was only about 14 hours. There
has never been so much activity at the
Varga
Service
Center
– ever! Tom, of Tom’s
Aircraft, spent many long hours working on this project. Steve of Steve’s Aircraft Service
provided a lot of insight as to how to work with the FAA. Approval for the second Varga came
within another twenty days.
I was told by more than one rep from the FAA that what we
achieved was rare and could never be done in less than a year. I’m sure this would have been true
had it not been for Max Bishop who was called upon many times for information
and we even called up retired aircraft engineers who I worked with before I
retired. The biggest thanks goes
to FAA Engineer Horsburgh as he provided guidance the entire time. There was a great deal of technical
data going back and forth between mechanic ranks and engineering gurus. Pat, of course, was doing all of the
correspondence for me so many thanks to her.
Max and I collaborated on producing a Service Bulletin for
Augustair and I want you to know it was 3 pages long, not the 22 pages that
were published. On the negative
side of all this, some individuals feel we created all this just to make this
miserable and to spend their hard-earned dollars. Guess you can’t make everyone happy!
The
following is Max Bishop's version of the Vertical Stabilizer issue:
Where it all started and
how and more than you ever wanted or needed to know…
I first learned about this problem
years ago while I
was Varga Aircraft's Engineering Manager just before Varga closed it's doors in
June of 1982…
When someone notified Varga of cracks in a
vertical stabilizer forward spar, on what I think may have been a Shinn, I
investigated the problem and submitted a report to the FAA describing what I had
learned and providing a potential solution, very similar I think, to what the
current Service Bulletin provides…
After the factory shut down, shop foreman
Al Wilson and I were running a sheet metal business out of Varga Aircraft's
hangar and I was still there when the report was returned to Varga with a reply from the FAA stating
that, since this was the only instance of cracks like these that they knew of
and that it should be detectable in a normal annual inspection, no further FAA
action would be taken unless and until there were more reports of similar
instances.
My report and the FAA letter may still
exist somewhere in Varga's archives but, at this point, it's existence is
irrelevant...
At the time, I was a bit worried that the
problem might resurface again some day but, since it was out of my hands, I had
no choice but to let it go...
In any event, I was not surprised to hear
about a crack when I got an email from Lee Beery but I was surprised to learn
that cracks had traveled across the spar web without being detected sooner. It
was fortunate that there was no catastrophic
failure in flight. Fortunately, this was discovered in time there was ample opportunity to warn Varga, Shinn and
Morrisey owners of the problem. That being the case, I think that I was not as alarmed as those who discovered
it or as was the FAA when they were first told. I will tell you why and
continue a discussion about the cause but first I will digress a bit to give you
a little perspective (both personal and historical) about cracks... Much of this
may seem unrelated to the current issue... but I'll get there... ;-)
In about 1978, I think, we began
to get reports of cracks in elevator control horn flanges on airplanes. After
some review of he reports it began to appear that most, if not all, of the
airplanes with cracks were being used in
flight schools or for rent by FBOs.
A service bulletin was issued requiring
25 hour mandatory inspections and an Airworthiness Directive soon followed.
One airplane owner was so concerned that
he brought his airplane to the factory for us to test. One of the first things
that we notices was that the aft fuselage was dented on each side. This
appeared to mean
that the elevator horn balance arms were vibrating very
severely from side to side. But when we did a vibration survey, flight tests
and load tests on the part, we couldn't find anything that showed the airplane
or parts were loaded or operating outside of the what original design data
said it should be and we could not repeat a vibration a severe as the ones
causing the aft fuselage dents...
Even though we couldn't duplicate the
problem at the time, we knew it was a serious issue so, on advice from n engineer whose opinion was respected
by the FAA we changed the elevator horn from aluminum to steel
to improve stiffness and strength. Vibration, flight and
load test data was about the same as with the aluminum part and after the
design change was accepted by the FAA, we started shipping replacement parts
to owners who found cracks.
Unfortunately, after we
began to ship the steel parts, even with the Service Bulletin and the AD in
effect, there was a fatal accident caused by the failure of an elevator
horn...
The airplane that crashed was one of
five being used by a company with a Navy contract to test Cadets for
suitability as pilots. My understanding was that each student got 15 hours of
instructed flight and if good enough, the Cadet was qualified to go on to Navy
flight school...
After we shipped new elevator horns to
the flight school so that they could continue their program, I got a call from
an FAA manufacturing inspector asking if I wanted to go to visit the flight
school to help him investigate the problem... I accepted and when we got
there, the first thing we did was review the aircraft logs and the four
elevator horns that were removed from the airplanes that had had them replaced
and were still in use. While the FAA guy examined the logbooks, I looked at
the elevator horns we had been given. The logbooks did have all had the
correct signoffs at the required 25 hour intervals. Unfortunately, though one
of the service bulletin requirements was to remove the paint in the flange
area in order to accomplish an inspection, first thing I noticed was that, on
none of the four remaining elevator horns, had the paint been removed.
After the FAA pointed this out to the
manager of the company, I was called into his office for a private
discussion... Apparently, he had called his lawyer to discuss the apparent
discrepancy between the logbooks and the parts and, upon legal advice, I was
told that, though I was allowed to stay on the premises, I would no longer be
allowed to examine the planes or parts while the FAA representative finished
his review so I wandered around in the fog on the ramp until it was time to go
home... ;-)
In the process of our search for a
solution, we hired a vibration specialist (a guy named Sandy) to analyze the
problem for us. Within a few days of our call to him, he came by with his test
equipment, instrumented the back end of an airplane with accelerometers and
strain gauges and climbed in the back seat with his recorder to do a flight
test. When he reviewed the flight test data on his analyzer he quickly
determined that the problem was a resonant frequency that was at about twice
the elevator's natural frequency of about 1200 cpm that was so strong during
an accelerated stall that the loads at the elevator horn flange, where the
cracks were occurring, were greater than either the aluminum or steel material
could handle over time. It turned out that the elevator horn/balance weight
assembly was a near perfect tuning fork when excited by an accelerated stall
when the engine speed was about 2400 rpm.
With this information in hand, Sandy
suggested a company that could do redesign of the part for us so we contracted
with them to do the job.
Sometime later, along with a bill for
$7,000, we were sent a drawing of a proposed elevator horn and balance arm
assembly that was made from solid 4130 steel that weighed twice as much as the
whole elevator.
Dismayed by the design I had in hand, I
called Sandy to tell him that this was unacceptable and ask him what I should
do... He told me that he had an out of state job to do in a couple of weeks
and, on his way back in his Twin Beech, if I would come up with a few
elevators designs that I thought might work, he would stop by and test them to
see which was the best...
By the time he got there, I had 5
different elevator horn designs for him to test. The simplest (cheapest) was
just an existing steel horn with gussets welded at each flange and the most
complicated (expensive) was the elevator horn design that you now have on your
airplanes. I don't remember what the 3 other variations were but I do remember
that the test Sandy did was simple, fun and interesting...
Once he had his analyzer set up on a
table in my office area, he had me attach each horn, in turn, to the table
with C-clamps and after he attached a couple of accelerometers to the horn, he
just whacked it with a hammer to see what it's natural frequency was...
After the whacking... errr... testing
was done, it was obvious to Sandy that any of the horns would work but, for
political reasons (both FAA and customer), it was decided to go with the
stiffest (and most expensive) design.
From there we proceeded in the next
couple of weeks to install a new horn on an airplane and have Sandy come back,
instrument the new horn and do a flight test... The result was that the stress
on the part went from over 90,000 psi in the old part to less than 10,000 psi in the
new...
With that data in hand, we got FAA
approval fairly quickly and began manufacturing and shipping the new parts as
fast as we could.
OK... what was the point of this long
preamble that apparently has nothing to do with the vertical stablizer? Well...
mostly it's about lessons learned about vibration, fatigue and stress but it's a
journey and I'll get there...
Here's another part of the
journey.
The Varga Taildragger was originally
designed and built by one of our dealers named Hibbard Aviation. In trying to
sell airplanes, Hibbard had gotten lots
of inquiries about a tailwheel Varga but, heavily into the certification process of
the Model 2180 Varga couldn't afford the time an energy required to build and
certify a taildragger as well so Hibbard chose to go the STC route and design
and build their own. It took many months but they were eventually able to
convert a Model 2150A tricycle gear plane to a taildragger and get it certified.
Interestingly, about the time that Hibbard finished there certification, a new partner in Varga
brought an infusion in cash that allowed us
to buy the tailwheel STC from Hibbard and add the 2150ATG to the 2150A and the
2180 model that had been recently certified.
Unfortunately, as it happened, the STC was for a 2150 and now, with the availability of
the model 2180, all of our customers with deposit money in hand, wanted a 180HP
taildragger instead of a 150HP one...
This meant that incorporating the taildragger
into the production line required the addition of the Model 2180 to the STC
and lots of extra work for Max and others.
LETTERS
& EMAILS
From:
Joseph M. Atkinson
Sent: Thursday, April 01, 2010 1:05 PM
To: mbishop5@cox.net
Subject: Completed Varga Stabilizer AD
Hi Max – in case you are keeping track, I just wanted
to let you know what we found on my Varga 8417J, a 1980 model 2150A.
There were a total of 3 small cracks. 2 were in the left side bend
radius, each about ½ inch in length, of negligible width and easily visible.
The 3rd crack was in the right side bend radius, about 3/16 in
length, and was so slight in width so as not to be visible until exposed by
the dye-penetrant.
Oddly, one of the left side cracks that was too low on
the bend radius to be visible in the initial visual pre-removal inspection had
previously been stop drilled. There was only a short, cryptic
reference in the aircraft log, from the 2002 annual inspection (I purchased
the airplane in 2005), that stated “Stop drilled crack in stabilizer”.
My A&P said that due to its location, the prior stop drill could not have
been performed without removing the vertical stabilizer. There was no
obvious evidence, either on the aircraft on in the logbook, that the tail had
ever been removed prior to this week. Moreover, that stop drill didn’t
seem to touch the metal splice plate in even the slightest way, despite
the fact that the splice plate lies flush against the spar in that location,
so the origin of that prior stop drill remains a mystery.
My A&P complied with the damage remediation
requirements in the service bulletin, and the aircraft is now ready to fly
again, which I hope to do this weekend. Thanks again for all of your
work in getting the word out.
Joe Atkinson
NEW MEMBERS:
PERSONAL NOTES:
Max
Bishop
I will continue provide the VG21
Newsletter on the web site and will expand and improve it as time and
circumstances permit. Those members who request it
will receive a hard copy.
Please don't hesitate to provide
suggestions for subject, content or format changes or corrections to this web
site or the newsletter at any time.
Questions and
com
ments about Vargas are always wel
com
e...
maxbishop@gowebay.com
or mbishop5@cox.net
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